Method of making stable color photographic prints

ABSTRACT

A method of making a photographic color print using a photographic color material containing low levels of silver halide characterized in that, 
     (a) after image formation and washing and/or stop bath treatment and 
     (b) before non-uniform exposure to adventitious light, 
     the print is uniformly exposed to a light source so that undeveloped silver halide is caused to print out uniformly. Such a uniform density is much more acceptable than a non-uniform density caused by uneven light in normal conditions.

This invention relates to a method of making stable photographic colourprints and particularly to making such prints with photographicmaterials that contain low levels of silver halide.

There have been many proposals to reduce the amount of silver halideemployed in photographic colour materials and colour print materials inparticular. One preferred method is to use the so-called redoxamplification processes.

Redox amplification processes have been described, for example inBritish Specification Nos. 1,268,126, 1,399,481, 1,403,418 and1,560,572. In such processes colour materials are developed to produce asilver image (which may contain only small amounts of silver) and thentreated with a redox amplifying solution (or a combineddeveloper-amplifier) to form a dye image. The developer-amplifiersolution contains a reducing agent, for example a colour developingagent, and an oxidising agent which will oxidise the colour developingagent in the presence of the silver image which acts as a catalyst. Thephotographic material used in such a process may be a conventionalcoupler-containing silver halide material or an image transfer materialcontaining redox dye releasers. Oxidised colour developer reacts with acolour coupler (usually contained in the photographic materialphotographic material) to form image dye. The amount of dye formeddepends on the time of treatment or the availability of colour couplerrather than the amount of silver in the image as is the case inconventional colour development processes. Examples of suitableoxidising agents include peroxy compounds including hydrogen peroxideand compounds which provide hydrogen peroxide, eg addition compounds ofhydrogen peroxide; cobalt (III) complexes including cobalt hexamminecomplexes; and periodates. Mixtures of such compounds can also be used.A particular application of this technology is in the processing ofsilver chloride colour paper, especially such paper with low silverlevels.

Photographic paper for redox amplification processes can be made withincreasingly low levels of silver halide. When the level is small enoughthe density of the developed silver is barely noticeable in the finishedprint. However over a period of time the undeveloped silver halideremaining in the paper tends to print out (ie the silver halide isreduced to visible silver image) non-uniformly due to the non-uniformnature of exposure by adventitious light. This non-uniform printout doestend to be noticeable when viewing the print.

According to the present invention there is provided a method of makinga photographic colour print using a photographic colour materialcontaining low levels of silver halide characterised in that,

(a) after image formation and washing and/or stop bath treatment and

(b) before non-uniform exposure to adventitious light,

the print is uniformly exposed to a light source so that undevelopedsilver halide is caused to print out uniformly.

The exposure can be at any stage after which further imagewise imageformation can occur. This will be, for example, when any developer hasbeen removed by washing or inactived by a stop bath.

The uniform silver image, in contrast to the non-uniform image normallyproduced by print-out over a period of time, is not noticeable whenviewing the print. The non-uniform exposure to light occurs because ofthe varied light conditions, degree of shading falling on differentparts of the picture at different times in its history, etc. Undernormal processing lab arrangements the prints are placed in packagingfor return to the customer very soon after coming off the "productionline" under ordinary room light conditions.

In a preferred embodiment the uniform exposure occurs before the printis delivered to the customer. It is convenient if the uniform exposuremeans is built into the processing machine used to make the print.

The uniform exposure is preferably accomplished in the processingapparatus using appropriately mounted exposure means such as tungstenbulbs or fluorescent tubes. Clearly no exposure of the photographicmaterial should occur before the development and/or amplification hasfully taken place. Such apparatus is known from the processing ofreversal films including reversal colour films of the "Kodachrome" typewherein separate light fogging of the red and blue-sensitive layer unitsis employed. Alternatively the finished print could merely be placeunder a uniform light source for a while before being packaged andreturned to the customer.

Preferably, the light source for the uniform exposure is anincandescent, fluorescent, arc or mercury lamp, electronic flash or thesun. The time of exposure to the uniform light should be sufficient thatall undeveloped silver halide is reduced to silver. Typically such atime is from 0.1 to 500 seconds, preferably from 1 to 100 seconds, morepreferably from 2 to 30 seconds. The optimum exposure time can bedetermined by experiment.

The advantages of the present process are that only the image-formingstep is needed while the traditionally needed bleach and/or fix stepscan be omitted; fewer processing tanks need be used; the provision ofthe exposing radiation is inexpensive and non-polluting; and theomission of the bleach and/or fix reduces the effluent from the process.

Preferably the image-forming process is a colour redox amplificationprocess employed hydrogen peroxide or a compound which provides hydrogenperoxide. The colour photographic material to be processed may be of anytype but will preferably contain low amounts of silver halide. Preferredsilver halide coverages are in the range 0.1 to 80, preferably 0.1 to20, particularly 0.1 to 3 mg/m² (as silver). The material may comprisethe emulsions, sensitisers, couplers, supports, layers, additives, etc.described in Research Disclosure, December 1978, Item 17643, publishedby Kenneth Mason Publications Ltd, Dudley Annex, 12a North Street,Emsworth, Hants P010 7DQ, U.K.

In a preferred embodiment the photographic material comprises aresin-coated paper support and the emulsion layers comprise more than80%, preferably more than 90% silver chloride and are more preferablycomposed of substantially pure silver chloride. Preferably theamplification solution contains hydrogen peroxide and a colourdeveloping agent.

The photographic materials can be single colour materials or multicolourmaterials. Multicolour materials contain dye image-forming unitssensitive to each of the three primary regions of the spectrum. Eachunit can be comprised of a single emulsion layer or of multiple emulsionlayers sensitive to a given region of the spectrum. The layers of thematerials, including the layers of the image-forming units, can bearranged in various orders as known in the art.

A typical multicolour photographic material comprises a support bearinga yellow dye image-forming unit comprised of at least one blue-sensitivesilver halide emulsion layer having associated therewith at least oneyellow dye-forming coupler, and magenta and cyan dye image-forming unitscomprising at least one green- or red-sensitive silver halide emulsionlayer having associated therewith at least one magenta or cyandye-forming coupler respectively. The material can contain additionallayers, such as filter layers.

Preferably the processing essentially comprises a singledeveloper/amplifier step or a developer step followed by amplifier ordeveloper/amplifier step. Optionally wash, stop and/or dry steps may beadded.

The following Examples are included for a better understanding of theinvention.

EXAMPLE 1

A developer amplifier was made up of the following formulation:

    ______________________________________                                        Potassium carbonate     25     g                                              1-hydroxyethylidene-1,1'-                                                     diphosphonic acid       0.6    g                                              diethyltriamine-pentaacetic                                                   acid                    0.6    g                                              Diethylhydroxylamine    5.0    g                                              Potassium chloride      1.35   g                                              4-N-ethyl-N-(b-methane-                                                       sulphonamidoethyl)-o-toluidine                                                sesquisulphate          3.5    g                                              Hydrogen peroxide 30%   10.0   g                                              Water to                1      liter                                          pH adjusted to 10.3 with sodium hydroxide solution                            ______________________________________                                    

A colour photographic silver chloride paper having a total silverchloride laydown of 55 mg/m2 (as silver) was used. A piece of this paperwas processed for 30 seconds at 40° C., in the above developeramplifier, without being exposed to light. The paper was then plungedinto a 5% acetic acid stop bath solution to prevent further development.The paper was then split into two pieces. One piece was exposed todirect sunlight for 5 minutes. When viewed without reference to otherstrips the stain of this print appeared acceptable. The other piece wasleft in subdued room light. The strips were then hung up to dry insubdued light.

The processed strips were put in a high intensity fading device, whichessentially meant placing the strips two inches away from lit daylightfluorescent bulb, with half the area of each strip covered with a pieceof black paper. The strips were held in position for two hours and thenthe neutral reflection density was measured. The results for the changesin density are shown below. They clearly show that the strip that hadbeen exposed to sunlight before completion of drying, experienced nofurther printout. The unexposed strip reached the same density of thepre-exposed strip only in the areas exposed to light. This left anundesirable density step at the edge of the shadowed area.

    ______________________________________                                                       Initial neutral                                                                          2 hr post                                                          density after                                                                            exposure                                            Treatment      processing neutral density                                     ______________________________________                                        NONE           0.14       0.17                                                sunlight exposed                                                                             0.17       0.17                                                ______________________________________                                    

We claim:
 1. A method of making a photographic colour print using aphotographic colour material containing low levels of silver halide,comprising:forming an image on the photographic colour material; washingthe photographic colour material and/or treating the photographic colourmaterial in a stop bath after said forming of said image; uniformlyexposing the photographic colour material to a light source after saidwashing and/or said treating, whereby undeveloped silver halide in saidphotographic colour material prints out uniformly; and non-uniformlyexposing the photographic colour material to adventitious light.
 2. Amethod according to claim 1, wherein said uniformly exposing is carriedout before said photographic colour material is delivered to a customer.3. A method according to claim 1, wherein said light source is anincandescent lamp, a fluorescent lamp, an arc lamp, a mercury lamp, anelectronic flash, or the sun.
 4. A method according to claim 1, whereinsaid uniformly exposing is carried out for a period of from 0.1 to 500seconds.
 5. A method according to claim 1, wherein said forming of saidimage comprises a redox amplification process.
 6. A method according toclaim 1, wherein the photographic colour material subjected to saiduniformly exposing is an unbleached, unfixed photographic colourmaterial.
 7. A method according to claim 1, wherein said photographiccolour material comprises silver halide at a total coating weight offrom 0.1 to 80 mg/m² as silver.
 8. A method according to claim 7,wherein said photographic colour material comprises silver halide at atotal coating weight of from 0.1 to 20 mg/m² as silver.
 9. A methodaccording to claim 7, wherein said photographic colour materialcomprises silver halide at a total coating weight of from 0.1 to 3 mg/m²as silver.
 10. A method according to claim 1, wherein said photographiccolour material comprises silver halide containing at least 80% silverchloride.
 11. A method according to claim 1, wherein said photographiccolour material comprises silver halide containing at least 90% silverchloride.